Such methods are being studied with increasing attention inasmuch as systems are being developed for the targeted distribution of information specifically intended for individuals specifically identified as being recipients, such targeted distribution being novel as compared with the functioning of traditional distribution systems entailing indiscriminate broadcasting of information such as audiovisual programs carried, for example, by radioelectrical signals transmitted by wireless.
Targeted distribution systems whose use is possible in the present state of the art generally make use of a conversion of an analog signal, representing stimuli to be transmitted, into a digital data signal. Said conversion is usually followed by an encoding of said data in order to reduce the volume as far as possible without thereby in any way causing this data to suffer significant deterioration. The encoded data is designed to be transmitted by packets according to standardized transmission protocols such as the Internet IPv4 or IPv6 protocols. It has to be recognized however that, although these packet transmission protocols offer considerable advantages, which is what has made them successful, they are intrinsically a source of deterioration caused by the inevitable loss of certain data packets. Furthermore, whatever the chosen encoding technique, its goal would be a compression that cannot be obtained except by eliminating certain characteristics, deemed to be superfluous, of the stimuli to be encoded. Such compression would inevitably generate losses which could have a negative impact on the perception that a recipient might have of the stimuli transmitted to him in encoded form.
Now an individual who, for example, has subscribed to a service of the supply of audiovisual programs will be contractually entitled to expect a minimum level of quality of the images and sounds that are transmitted to him or her, so that a provider of this supply service would have to ensure that such demands are properly met. This cannot be achieved except by carrying out a relevant evaluation of the quality of the stimuli which will be restored to the recipient after transmission. This evaluation would have to be done in taking account of the specific human features of this recipient's faculties of perception.
Various methods have already been elaborated for the separate evaluation of a spatial quality and a temporal quality of a signal bearing a stimulus, such a moving picture or a sound. These methods make use for example of a group of persons each of whom has to be exposed to said stimulus and is then requested to assign a representative grade to its spatial quality (for example the sharpness of a picture or the absence of distortion in the sound) or temporal quality (for example the fluidity of a moving picture or the absence of a phase shift between two channels of a stereophonic signal) as this person would have perceived it. However, such methods require major logistics and are therefore costly to implement since they require that a sufficient number of persons should be brought together in a controlled environment such as a test laboratory so that a statistical mean of the grades assigned is effectively representative of a mean perception. Furthermore, such methods cannot be used for real-time measurement of quality as perceived by a subscriber at the reception of a stream of stimuli that he would have commanded, so that these methods are not adapted as such to quality control applications in the above-described systems for the targeted distribution of information.
It has also been noted that, in the implementation of such methods, the perception that a person might have of the spatial quality of a stimulus cannot be totally decorrelated from the perception that this very same person has of the temporal quality of said stimulus and vice-versa, during an evaluation of an overall quality as perceived by this person. For example, for a person viewing a video sequence with subjects having movements of wide amplitude, a reduction of an image frequency of said sequence would not improve the total quality as perceived by this person.
A technique of correlation of the spatial and temporal qualities has thus been designed to take account of the correlation made of it by a recipient of the stimuli considered. This technique consists in taking the product between parameters representing these spatial and temporal qualities in isolation. Such a multiplier approach however has not been rigorously validated in the prior art.
Work by the inventors however has demonstrated that a simple multiplication of parameters representing these spatial and temporal qualities in isolation was not enough to take account of the correlation process implemented by the human recipient. This work has made it possible especially to note that the perception by a person of a variation of a quality parameter when the other parameter is kept constant is not linear. This is enough to demonstrate that the multiplier approach described here above is not relevant.